Experiment Spokesman Goal Running time

Thesis?

Scissors Mode Tonchev Analyze Scissors Mode excitations in actinide nuclei

500@

Pgymy Dipole Tonchev Analyze evolution of Pygmy Dipole resonance as a function of deformation

500

IVGQR Ahmed, Weller

Analyze IVGQR in A=30-200 nuclei evaluation resonance energy, width and EWSR – and compare with theory

500 2-3

Structure Experiments – at HIGS

@ 300 hrs are paid by DNDO

The Frontiers of Nuclear Science – A Long Range Plan (2007)

[LRP, Nuclei: From Structure to Exploding Stars- What is the Origin of Simple Patterns in Nuclei, p 65]

“

”

2-phonon excitations:

⊗1-

Found at sum energy of one-phononstates: ~ 3 MeV

Found usuallybetween 2.7-3.6 MeV

Proton-Neutron symmetric Existence because of nuclear 2-fluid system

⊗2+FS 2+

MS

1+

Dipole Excitation Below 4 MeV: Scissors Mode Tonchev

Scissors mode systematics: clearly collective Degree of fragmentation depends on deformation

Dipole Excitation Below 4 MeV

Proposed Experiments

Where we are going: study the scissor mode in actinide nuclei

1. Completed experiments: 235U, 238U, 232Th.

2. To be measured: 239Pu, 237Np, 233U.

3. Working with the theorist to develop a model (RPA-based) to reproduce all experimental observables of the E1 and M1

excitations for actinides nuclei.

Interpretation of the Pygmy Resonance in QPM calculations Tonchev

PDR is predominantly E1 mode of excitation

PDR is enhanced strength below the GDR

We unveiled the fine structure of the M1 spin-flip mode

Evidence for surface neutron density oscillations

“Soft dipole mode“ at ~7 MeV is mixture of isoscalar and isovector components

N. Tsoneva, H. Lenske, PRC 77, 024321 (2008), A.P. Tonchev et al. NIM B 241, 51474 (2005); A.P. Tonchev et al. AIP 819, 350 (2006); AIP 1090, 74 (2009); A.P. Tonchev et al. PRL 104 072501 (2010).

p n

What we have learned ?

Fine and Gross Structure of the PDR in 138Ba

A. Tonchev et al., PRL 104, 072501 (2010)

Fine structure Gross structure

Pygmy Dipole Resonance Impact

Nuclear astrophysics: r-process 1998 S. Goriely PLB2003 M. Arnold et al. PR2005 T. Rauscher NPA

Neutrino-less double-beta decay physics2004 J. Bahcall et al. PRD

Extract the γ-ray transition matrix elements for the decay (QRPA)

Study of the structure difference of the initial and final states

Study of the nuclear dipole response in 76Se and 76Ge isotopes

Testing the nuclear models for stable and extrapolating to exotic nuclei1998 S. Goriely, PLB; 2008 G. Rusev ,PRC

Neutron radius: PDR provides experimental constrains on properties of nuclear matter (neutron skin and symmetry energy)

2006 Piekarewicz PRC

124Xe

Present Experimental Activity with N=82 Nuclei

130XeZ=54

N=8

2

138Ba

140Ce

142Nd

144Sm

Completed measurements at HIGS

p,n n

N/Z

1.32

1.37

1.41

1.46

154Sm154Sm

2

0.09

0.10

0.09

0.09

Proposed measurements

136Xe132Xe

• Predicted dependence on N/Z ratio weak isospin effect

134Xe

B(E1) [10-3e2fm2]

536

576

600

960

Proposed Experiment

1. PDR as a function of deformation 144 148 152 154 Sm62

N/Z 1.32 1.39 1.45 1.48 ↑

2 0.09 0.14 0.31 0.34 ↑

Increased deformation with N/Z

128 130 132 134 136 Xe54

N/Z 1.37 1.41 1.44 1.48 1.52 ↑

2 0.18 0.17 0.14 0.12 0.09 ↓

Decreased deformation with N/Z

F. Dönau et. al. PRC 76, 014317 (2007); G. Rusev et al. PRC 73, 044308 (2006); G. Rusev et al., PRC (2009)

QRPA calculations

N

PDR region

An example – 209Bi

IVGQR

odd± (E)

Weller, Ahmed

209Bi Results

209Bi Results – Notice Quality of Our data

209Bi Results – Notice Quality of Our data